Ford Motor Company has utilized transmission model numbers 4R70E/W and 4R75E/W in a large number of its vehicles since the 1990s, including in many of its most popular lines of cars. FIG. 6 illustrates an exemplary Original Equipment (OE) forward drum 600 typical of those used in Ford's 4R70E/W and 4R75E/W transmissions, FIG. 6 showing the drum assembled with OE stator tube 602 and piston 608. As shown, OE drum 600 includes clutch pack portion 604 configured to house a clutch pack (not shown), piston portion 606 configured to house piston 608, and stator tube portion 610 configured to couple with OE stator tube 602. Clutch pack portion 604 includes snap ring groove 609 that, when assembled, houses a snap ring (not shown) that is configured to prevent the clutch pack from moving axially within the drum. During operation, OE drum 600 is configured to rotate around OE stator tube 602. To apply the forward clutch, pressurized oil is transmitted from OE stator tube 602 to piston cavity 612 formed between piston 608 and sidewall 614, the pressurized oil forcing the piston against the clutch pack to apply the clutches. Oil is transmitted via OE stator tube flow passageway 616, the oil flowing from the flow passageway into a first oil feed plenum 618 defined by groove 619 formed around the circumference of the stator tube. Seals 621 maintain a seal between tube 602 and drum 600, and ball 623 blocks oil from escaping from the end of flow passageway 616, such that oil is forced into first plenum 618. Stator tube portion 610 of OE drum 600 includes a plurality of oil feed bores 622 extending linearly between first oil feed plenum 618 and piston cavity 612 to provide fluid communication between the oil feed plenum and piston cavity. During manufacturing, OE drum 600 is constructed by welding clutch pack portion 604 and piston portion 606 to stator tube portion 610 at weld location 620. Oil feed bores 622 are drilled before the two portions are welded because after the drum is welded, the clutch pack portion 604 extends across the drill path for forming bores 622, such that drilling bores 622 after welding the two portions together would not be easily achievable without an appreciable increase in manufacturing costs, for example, requiring specially-designed tooling.
The 4R70E/W and 4R75E/W clutch drums fail in a relatively high number of vehicles at snap ring groove 609. Specifically, the sidewall of the clutch drum separates at the snap ring groove. Despite these transmissions being in widespread use since the 1990s, and despite all of the failures that continue to this day, no replacement drums exist that provide an adequate solution to the problem. Instead, transmission repair businesses are forced to either weld the broken drum back together, which can only be done once or twice before further re-welds are not possible, or the repair business must buy a new OE drum having the same tendency to fail.